Fifth generation (5G) wireless communication systems are envisaged to expand usage scenarios and applications with respect to current mobile network generations. Ultra-Reliable Low-Latency Communications (URLLC) with strict latency and reliability requirement was agreed as one key scenario for 5G communication systems. URLCC demands an ultra-high delivery reliability of 99.999% (five nines) or even higher within a delivery latency bound as low as half a millisecond. URLLC is relevant for establishing a range of application including:                Intelligent transportation systems of connected cars;        Monitoring of smart grids with distributed renewable energy sources;        Factory automation with communication among actuators, sensors and controllers;        Drone control and aircraft communication; and        Remote surgery, remote machine operation, etc.Each scenario might require a different set of latency and reliability requirements, e.g., 3-5 ms latency with 1-10−5 reliability for smart grids, and 1 ms latency with 1-10−9 reliability for factory automation, etc.        
With respect to Long Term Evolution (LTE) uplink (UL) transmissions, a wireless device (WD), such as, for example, a user equipment (UE) waits for the next transmission opportunity to send a scheduling request. Afterwards, a network node, such as, for example, an evolved Node B (eNodeB or eNB) allocates a set of resources to the wireless device. As one part of the URLLC requirements, some standardization work has been done in LTE rel-14 and are on-going for LTE rel-15 to reduce latency down to the sub-millisecond range.
In order to remove the latency due to the waiting time of the scheduling request, UL semi-persistent scheduling (SPS) has been has been standardized since LTE rel-18. IUA pre-allocates the transmission resources to the wireless device in anticipation of possible packet transmissions. In rel-14, SPS was enhanced such that wireless devices do not use the allocated resource to transmit data if the wireless device does not have any packet to transmit. IUA also enhances the WD battery life by avoiding uplink transmissions in case there is nothing to transmit in the WD transmit buffer while avoiding uplink interference.
Another approach to address latency reductions is to reduce the transport time of data and control signaling, by reducing the length of a transmission time interval (TTI), i.e., the smallest scheduling unit. This is called a short transmission time interval (sTTI). In addition, the delivery delay can be reduced, due to a smaller waiting time for sending a scheduling request. Also, SPS enhancements together with sTTI would also enable reducing the latency even further.
Preconfigured grants, including SPS are considered as one component to achieve low latency by pre-assigning uplink resources to the WD. The latency is reduced by skipping the requirement of scheduling requests from the WD to send uplink data. The problem with configured grants is that they consume dedicated uplink resources that are not shared. In most cases even for latency critical scenarios, the WD traffic pattern is sporadic so most dedicated resources are wasted.